Historical clue formulations

• Seasonal thinning in the atmosphere over Antarctica — 2017-02-20
• Opening for an E.P.A. worker? — 2016-08-27
• Atmospheric problem — 2015-05-29
• Antarctic environmental concern — 2008-05-10
• Opening on an environmentalist's agenda? — 2008-02-08
• Problem linked to CFC's — 2005-09-15